Physical Chemistry
- Created by: fjhcab
- Created on: 04-01-16 10:57
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- Enthalpy
- Basics
- Exothermic gives out heat delta H is NEGATIVE. Bond Making
- Endothermic takes in heat delta H is POSITIVE. Bond Breaking
- Combustion is always exothermic
- q=mc(delta T)
- q-enthalpy change
- c-specific heat capacity of water
- delta T-change in temperature
- m-mass of water
- Gradient=change in y/change in x
- rate of reaction= amount of reactant used or product formed/time
- Standard enthalpy change of formation
- Enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions
- Products-Reactants
- Standard enthalpy change of reaction
- Enthalpy change when the reaction occurs in molar quantities shown in the chemical equation, under standard conditions
- Standard enthalpy change of combustion
- Enthalpy change when 1 mole of substance is completely burned in oxygen, under standard conditions
- Reactants - Products
- Standard enthalpy change of neutralisation
- Enthalpy change when an acids and an alkali react, under standard conditions to form 1 mole of water
- Reaction Rates
- Increasing temperature speeds up reactions
- Particles have more kinetic energy so will move faster colliding more
- Increasing pressure speeds up reactions
- At higher pressures particles will be closer together increasing the chance of successful collisions
- Catalysts can speed up reations
- Lower activation energy. If activation energy is lower more particles will have enough energy to react
- Increasing concentration speeds up reactions
- Particles closer together so will collide more frequently
- Increasing temperature speeds up reactions
- Catalyst
- Provide an alternative reaction pathway with a lower activation energy
- Chemically unchanged at the end of the reaction
- Can be hetero or homo geneous
- Hetero- Catalyst is in a different phase from the reactant. Increases the surface area of the catalyst increase the amount that can react, increasing the rate of reaction
- Homo-Catalysts are in the same phase as the reactants. Forms an intermediate species when the reactants combine with the catalyst. which reacts to form the products and reform the catalyst
- Industry- lower production costs, gives more product in a shorter time & makes better products
- Less CO2 produced, energy is saved &fossil fuel reserves are preserved
- Dynamic Equilibrium
- If position of equilibrium moves to the left more reactants
- If position of equilibrium moves to the right more products
- Le Chatelier's Principle
- If pressure increases equilibrium will shift to the side with fewer gas molecule. If decreased the equilibrium will shift the idea with more gas molecules
- If concentration of reactants increase equilibrium will shift to the right to make more products. If concentration of products increases equilibrium will shift to the left to make more reactants
- If there's a change in concentration, pressure or temperature the equilibrium will move to counteract the change
- If temperature is increase equilibrium will shift to the endothermic direction. If temperature is decreased equilibrium will shift in the exothermic direction
- Catalyst have NO EFFECT
- Conditions in industry are a compromise. Lower temperature mean a slower rate of reaction, high pressures are expensive as you need stronger pipes and containers.
- Equilibrium Constant
- When you have a homogeneous reaction thats reached equilibrium you can work out a equilibrium constant Kc
- aA+bB dD+eE
- Kc=[D]d [E]e/ [A]a [B]b
- H2+I22HI Kc=[H]2/[H2]1 [I2]1
- =[H]2/[H2][I2]
- Substitue in values for H & I
- =[H]2/[H2][I2]
- H2+I22HI Kc=[H]2/[H2]1 [I2]1
- Kc=[D]d [E]e/ [A]a [B]b
- aA+bB dD+eE
- When you have a homogeneous reaction thats reached equilibrium you can work out a equilibrium constant Kc
- Basics
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